Re: [R] Help w/ matrix calc

From: James MacDonald <jmacdon_at_med.umich.edu>
Date: Fri 30 Jul 2004 - 00:36:40 EST


For row or column means with a matrix of any size, you will be much better served by using
rowMeans()
colMeans()

Best,

Jim

James W. MacDonald
Affymetrix and cDNA Microarray Core
University of Michigan Cancer Center
1500 E. Medical Center Drive
7410 CCGC
Ann Arbor MI 48109
734-647-5623

>>> Adaikalavan Ramasamy <ramasamy@cancer.org.uk> 07/29/04 09:04AM >>>

> m <- matrix( 1:12, nc=3 )
> m

     [,1] [,2] [,3]

[1,]    1    5    9
[2,]    2    6   10
[3,]    3    7   11
[4,]    4    8   12

> apply(m, 1, mean) # row means
[1] 5 6 7 8

> apply(m, 2, mean) # column means
[1] 2.5 6.5 10.5

Replace 'mean' with 'var' if you want variances instead.

On Thu, 2004-07-29 at 12:38, eesteves@ualg.pt wrote:
> Dear All,
> Help is needed! I have a matrix with frequencies of fish larvae per
length
> class (var. sl) and age-group (var. median.no) obtained with
>
> >k<-table(cut(sl,(5:22)),median.no)
> >k[2:5,1:5] #to ilustrate k
>
> 4 5 6 7
> (6,7] 3 1 0 0
> (7,8] 3 0 1 0
> (8,9] 3 4 3 5
> (9,10] 3 15 7 13
>
> from this matrix I would like to obtain the mean age per length class
i.e.
> vector of line means. How can I do this? If, instead of the means I
wanted the
> variances, how could I do it?
> Thanks in advance,
> Eduardo Esteves
>
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https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jul 30 00:48:12 2004

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